Abstract

4070

DRH rats are highly resistant to chemically-induced hepatic carcinogenesis. This strain was established by inbreeding the closed colony of Donryu rats for more than 20 generations under the continuous feeding of 3’-methyl-4-dimethylaminoazobenzene. When DRH rats were treated with hepatic carcinogens, the hepatic tissue shows less histological damage, indicating that their hepatocytes are resistant to the stress imposed by toxic chemicals. On the other hand, the culture conditions is known to provide great stress and induce oxidative damage in primary hepatocytes. We therefore compared the hepatocytes of DRH and Donryu rats under the primary culture conditions. Hepatocytes were isolated by the collagenase-perfusion method at 9 weeks of age either from DRH or Donryu rats and cultivated on collagen-coated dishes in the medium containing 10% FBS, EGF and insulin. DRH hepatocytes exhibited lower proliferation, less cell spreading and fewer apoptosis as compared to Donryu hepatocytes. Cyclin D was activated at much lesser degree in DRH hepatocytes as compared to Donryu hepatocytes, while cyclin E activation was not different. However, there was no difference according to the levels of 8-hydroxyguanine (8-OHG), a marker for the oxidative DNA damage, between DRH and Donryu hepatocytes. In addition, total reactive antioxidant potential of DRH liver homogenates was not much different as compared to Donryu liver homogenates. On the other hand, although ASK1 (apoptosis signal-regulating kinase, a kind of MAPKKK) is activated in both DRH and Donryu hepatocytes, while its downstream kinases, JNK and p38, were activated to much lesser extent in DRH hepatocytes than Donryu hepatocytes, suggesting that DRH hepatocytes may contain some inhibitor(s) that prevent the stress activating kinase pathways. Low degree of activation of stress activating kinases under the stressful conditions may result in low degree of apoptotic death of hepatocytes and thereby generation of low growth stimuli within the hepatic tissue, which may be related to the resistance to hepatic carcinogenesis in DRH rats. (Supported by the grants from the Japanese Ministry of Education, Culture, Sports, Science and Technology, and from the Japanese Ministry of Health, Labour and Welfare.)